Method of producing a semiconductor device with protruding contacts

ABSTRACT

A wiring ( 3 ) comprising electrical conductors ( 4, 5, 6, 7 ) is formed in a dielectric layer ( 2 ) on or above a semiconductor substrate ( 1 ), an opening is formed in the dielectric layer to uncover a contact pad ( 8 ), which is formed by one of the conductors, and a further opening is formed in the dielectric layer to uncover an area of a further conductor ( 5 ), separate from the contact pad. The further opening is filled with an electrically conductive material ( 9 ), and the dielectric layer is thinned from a side opposite the substrate, so that the electrically conductive material protrudes from the dielectric layer.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 5,767,001 discloses a semiconductor device forthree-dimensional integration, which comprises contact pins penetratinga substrate and protruding from a rear surface.

U.S. Pat. No. 5,910,020 discloses a production method for semiconductordevices by forming a tungsten pillar on a wiring and applying analuminum alloy to contact top and side surfaces of the tungsten pillar,which extend above a silicon oxide layer.

EP 2554980 A1 discloses an integrated circuit with sensor, whichcomprises a substrate with a stack of patterned metal layers insulatedfrom each other by dielectric layers. An upper metal layer comprises afirst electrode, a second electrode, a bond pad and a heating element.

U.S. 2009/0200664 A1 discloses a manufacturing method of semiconductordevices comprising a wafer, an SiN passivation film and a polyimidefilm. Metal layers include electrode pads of aluminum on the surface ofthe semiconductor wafer, especially a bonding pad, wiring layers, whichextend above the polyimide film, and solder bumps. Some of the wiringlayers are elongated in a substantially rectangular shape.

The publication of M.-S. Wang et al.: “Interface Dynamic BehaviorBetween a Carbon Nanotube and Metal Electrode,” in Advanced Materials 22(2010), pages 93 to 98 describes a contact between individual carbonnanotubes (CNTs) and sharpened tungsten electrodes. The tip-end of theelectrode absorbs the source CNT atoms, which then penetrate deep intoits body, form a carbide, and finally precipitate as freshly formedgraphitic tubular shells encapsulating the electrode.

SUMMARY OF THE INVENTION

The semiconductor device comprises a semiconductor substrate, adielectric layer on or above the substrate, a wiring comprisingelectrical conductors arranged in the dielectric layer, and a contactpad formed by one of the conductors. A further conductor of electricallyconductive material is arranged in the dielectric layer in contact witha further one of the conductors, separate from the contact pad. Thefurther conductor protrudes from the dielectric layer on a far side ofthe dielectric layer with respect to the substrate.

The semiconductor device may further comprise a passivation layer on thefar side of the dielectric layer, so that the further electricalconductor also protrudes from the passivation layer. The passivationlayer and the dielectric layer may comprise different materials. Inparticular, the dielectric layer may be a silicon oxide like SiO₂ andthe passivation layer a silicon nitride like Si₃N₄, for instance.

In particular, the further conductor may have the shape of an elongateridge with a longitudinal extension. The ridge may typically have alength along its longitudinal extension and a width transverse to itslongitudinal extension, the length being at least three times the width.The further conductor may protrude by a height in the range from 20 nmto 100 nm. The further conductor may comprise a plurality of singleconductors. Each of the single conductors may have the shape of anelongate ridge with a longitudinal extension, and the longitudinalextensions may especially be parallel to one another. The furtherconductor may comprise tungsten or copper.

A via hole may penetrate the semiconductor substrate, and ametallization may be arranged in the via hole in contact with one of theconductors, thus forming a through-substrate via.

The method comprises forming a wiring of electrical conductors in adielectric layer on or above a semiconductor substrate, an opening inthe dielectric layer to uncover a contact pad, which is formed by one ofthe conductors, and a further opening in the dielectric layer to uncoveran area of a further one of the conductors, separate from the contactpad. The further opening is filled with an electrically conductivematerial, and the dielectric layer is thinned from a side opposite thesubstrate, so that the electrically conductive material protrudes fromthe dielectric layer.

In a variant of the method, the electrically conductive material is alsofilled in the opening uncovering the contact pad, and a portion of theelectrically conductive material is removed such that a spacer is formedin the opening by a residual portion of the electrically conductivematerial while the further opening remains at least half filled.

In a further variant of the method, the further opening is formed by atrench.

In a further variant of the method, the further opening is formed by aplurality of parallel trenches.

In a further variant of the method, the electrically conductive materialfilling the further opening comprises a metal that is different from theelectrical conductors.

The following is a detailed description of examples of the productionmethod in conjunction with the appended figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section of a semiconductor device.

FIG. 2 is a cross section according to FIG. 1 including an arrangementof nanotubes.

FIG. 3 is a top view of the device according to FIG. 1.

FIG. 4 is a top view of the arrangement according to FIG. 2.

FIG. 5 is a cross section of an intermediate product of the productionmethod.

FIG. 6 is a cross section according to FIG. 5 after the application ofan electrically conductive material.

FIG. 7 is a cross section according to FIG. 6 after a partial removal ofthe electrically conductive material.

FIG. 8 is a cross section of a further semiconductor device comprising athrough-substrate via.

DETAILED DESCRIPTION

FIG. 1 is a cross section of a semiconductor device comprising asemiconductor substrate 1, which may be silicon, for instance, adielectric layer 2 on the semiconductor substrate 1, and a wiring 3embedded in the dielectric layer 2, which may be a silicon oxide,especially silicon dioxide, for instance. The wiring 3 compriseselectrical conductors, which may especially be formed by structuredmetal layers 6 and vertical interconnections 7 like metal plugs, forinstance. The wiring 3 may be provided for an integrated circuit like aCMOS circuit integrated in the semiconductor substrate 1. A contact pad8 is formed by one of the electrical conductors 4, which may typicallybelong to an uppermost metallization layer.

A further one of the electrical conductors 5, which is separate from thecontact pad 8, is provided with a further electrical conductor 9, whichprotrudes from the dielectric layer 2 on the far side with respect tothe semiconductor substrate 1. A passivation layer 10, which canespecially be formed from a material different from the material of thedielectric layer 2 and may comprise a silicon nitride like Si₃N₄, forinstance, can be applied on the dielectric layer 2 as shown in FIG. 1.If a passivation layer 10 is present, the further conductor 9 alsoprotrudes from the passivation layer 10. The height h by which thefurther conductor 9 protrudes may be typically in the range from 20 nmto 100 nm. The contact pad 8 may be provided in standard fashion withfurther electrically conductive material like an underbump metallization18, for instance.

FIG. 2 is a cross section according to FIG. 1 and schematicallyindicates an arrangement of the semiconductor device with a furtherdevice, which may especially be a gas sensor, a chemical sensor or ahumidity sensor, which may be provided with a gas-sensitive materiallike SnO₂ or carbon nanotubes. FIG. 2 shows a parallel arrangement ofnanotubes 11 contacting the protruding tips of the further conductor 9,by way of example.

FIG. 3 is a top view of the semiconductor device according to FIG. 1.The location of the cross section shown in FIG. 1 is indicated in FIG. 3by the horizontal dash-dotted line. Elements shown in FIG. 3 thatcorrespond to elements shown in FIG. 1 are designated with the samereference numerals. The contact pad 8 is formed by the electricalconductor 4, which is partially covered by the dielectric layer 2 and/orthe passivation layer 10. The outlines of the electrical conductor 4 andthe further electrical conductor 5 are shown in FIG. 3 by broken linesas hidden contours. The positions of the vertical interconnections 17that are connected to the electrical conductor 4 and the furtherelectrical conductor 5 are also indicated in FIG. 3. In thesemiconductor device according to FIGS. 1 and 3, the further conductor 9comprises a plurality of single conductors 19, each of which has theshape of an elongate ridge 12 with a longitudinal extension e. Thelongitudinal extensions e may especially be parallel to one another. Theridges 12 may all have the same size or may instead have differentsizes, as shown in FIG. 3 by way of example. The length d of a ridge 12,measured along its longitudinal extension e, exceeds its width wtypically by a factor of at least three.

FIG. 4 is a top view of the arrangement according to FIG. 2 and showsthe arrangement of the nanotubes 11 extending across the singleconductors 19 forming the further conductor 9. The other elements shownin FIG. 4 correspond to the elements shown in FIG. 3 and are designatedwith the same reference numerals. The parallel arrangement of the ridges12 forming the single conductors 19 and the transverse parallelarrangement of the nanotubes 11 may facilitate the connection of thenanotubes 11 with the further conductor 9.

FIG. 5 is a cross section of an intermediate product of the productionmethod. The semiconductor substrate 1 is provided with the dielectriclayer 2 including the wiring 3. FIG. 5 does not show the passivationlayer 10, which can optionally be applied on the dielectric layer 2 anddoes not essentially change the method steps. An opening 13 is formed inthe dielectric layer 2 to uncover a contact pad 8 formed by one of theconductors 4, and a further opening 14 is formed in the dielectric layer2 to uncover an area of a further one of the conductors 5, separate fromthe contact pad 8. The opening 13 and the further opening 14 can beformed in the same method step, especially by using a mask with windowsin the areas where the opening 13 and the further opening 14 are to beformed. In particular, the further opening 14 may be a plurality ofparallel trenches, for example. The length of the trenches is largerthan the width of the trenches, typically by a factor of at least three.

FIG. 6 is a cross section according to FIG. 5 after the application ofan electrically conductive material 15, especially a material comprisinga metal like tungsten or copper, which may form an entire layer. Beforethe electrically conductive material 15 is applied, a thin liner, whichmay be TiN, for instance, and is not shown in FIG. 6, may be applied onthe entire surface that is to be covered by the electrically conductivematerial 15. The further opening 14 is filled with the electricallyconductive material 15, which thus forms the further conductor 9. Theupper portion of the electrically conductive material 15 covering theupper surface of the dielectric layer 2 (or the passivation layer 10, ifsuch is provided) is then removed. This may be effected by etching theelectrically conductive material 15 selectively with respect to thedielectric layer 2 (or the passivation layer 10, if such is provided)and/or the liner, in particular by reactive ion etching (RIE). Theetching step may produce slight depressions in the area of the furtheropening 14, which however remains at least half filled. The upperportion of the electrically conductive material 15 can instead beremoved by chemical mechanical polishing (CMP), which yields anessentially planar surface with the further opening 14 remainingcompletely filled.

FIG. 7 is a cross section according to FIG. 6 after the removal of theupper portion of the electrically conductive material 15 by selectivelyetching. The etching step may be performed anisotropically, so that aspacer 16 consisting of a residual portion of the electricallyconductive material 15 is produced at the sidewall of the opening 13above the contact pad 8. The dielectric layer 2 (or the passivationlayer 10, if such is provided) is then thinned from the surface oppositeto the semiconductor substrate 1, until the further conductor 9protrudes from the dielectric layer 2 sufficiently far, and anembodiment similar to the one shown in FIG. 1 is thus obtained.

By the described method the semiconductor device can be produced withina standard CMOS process with only few additional method steps, which arefurthermore fully compatible with the standard CMOS process. Theprotruding further conductor 9 facilitates an electrical connection toelements of a further device, especially to elements comprising agas-sensitive material, like carbon nanotubes, for instance.

FIG. 8 is a cross section of a further semiconductor device comprising athrough-substrate via. A via hole 20 is etched from the rear side intothe semiconductor substrate 1, and a rear contact area of one of theconductors 6 of the wiring 3 is uncovered. A further dielectric layer 21is formed to insulate the semiconductor material. A metallization 22 isarranged in the via hole 20 in contact with the rear contact area of theelectrical conductor 6 of the wiring 3. The metallization 22 can beelectrically connected with a further rear contact area 23 on a rearportion of the metallization, which is provided for an externalelectrical connection. Thus an electrical interconnection penetratingthe semiconductor substrate 1 is formed. A further passivation layer 24,which is opened above the contact area 23, may be applied on the rearside and on the metallization 22 within the via hole 20.

1. A method of producing a semiconductor device, comprising: forming awiring comprising electrical conductors in a dielectric layer on orabove a semiconductor substrate; and forming an opening in thedielectric layer to uncover a contact formed by one of the conductors;forming a further opening in the dielectric layer and thus uncovering anarea of a further one of the conductors, separate from the contact pad;filling the further opening with an electrically conductive material,and thinning the dielectric layer is thinned from a side opposite thesubstrate, so that the electrically conductive material protrudes fromthe dielectric layer.
 2. The method of claim 1, wherein the electricallyconductive material is also filled in the opening uncovering the contactpad; and a portion of the electrically conductive material is removedsuch that a spacer is formed in the opening by a residual portion of theelectrically conductive material and the further opening remains atleast half filled.
 3. The method of claim 1, wherein the further openingis formed by a trench.
 4. The method of claim 1, wherein the furtheropening is formed by a plurality of parallel trenches.
 5. The method ofclaim 1, wherein the electrically conductive material filling thefurther opening comprises a metal that is different from the electricalconductors.